I’m actually now shooting with a Canon EOS Digital Rebel XTi, but I could still use an upgrade and some better lenses.
But I looked up your Canon EOS Digital Rebel XTi at dpreview.com ( a great website) and your Canon seems 'more than adequate' (joking). Except for not having Spot Metering and no programmable Auto ISO, it seems to have the same 'stuff' as my Nikon D3000 (my LCD screen is a bit larger at 3").
But if you don't already have a long zoom I'd check that Sigma Lens out at B&H. The glass is excellent, the pics are A-One and I really love mine.
And I really like that photo on your About Page. When the weather cools a tad where I'm at there's a Forest Preserve near me than I'll being going to, to hopefully get a shot similar. (I love Nature Photography)
And while there to teach the wife how to use her Nikon P100 I bought her for her B-Day. It's easy to use, has a 26x Zoom and other great features, and she doesn't have to worry about changing lenses. And her P100 also takes HQ Videos. Something I DON'T want any of my DSLRs, and why I choose the D3000 over the D3100 and D5000.
Anywho, Good Shooting, and have a great day.